This invention relates to a valve arrangement associated with a vehicle servo-steering mechanism of the rack and pinion type.
Servo-steering mechanisms of the foregoing type include a non-rotatable rack, a double acting piston and a piston rod attached to the piston and projecting externally of the housing within which the piston is reciprocably mounted. A distributing valve for controlling the supply and exhaust of pressurized fluid in response to axial movement of the rack, causes axial displacement of the piston.
A prestressed spring yieldably holds the distributor valve in a neutral position. Such a distributor valve arrangement in a servo-steering mechanism is already known, as disclosed for example in German Pat. No. AS 1137328. The double acting piston in such mechanism forms part of the distributing valve. However, the piston is disposed in symmetrical relation to the rack driving pinion so that two piston operating surfaces of equal size are exposed to pressurized fluid under control of a valve mechanism having a single intake from a pump and a single return port to the reservoir tank. One of the disadvantages of such an arrangement resides in the difficulty in maintaining a proper neutral setting for the distributor valve.
According to the disclosure in German Pat. No. OS 2,000,377 a valve arrangement for a vehicle servo-steering mechanism also includes a portion of the servomotor piston as part of the distributor valve. Unlike the disclosure in German Pat. No. AS 1137328 aforementioned, however, the latter patent features as a valve element that is displaced relative to the rack driving pinion, as a result of which two operating chambers associated with a piston exert a differential piston actuating force by virtue of opposite piston surfaces of different surface area. The latter arrangement, however, also suffers from the same problem aforementioned, namely difficulty in maintaining a proper neutral setting for the distributor valve.
It is therefore an important object of the present invention to provide a valve controlled servo-steering mechanism of the aforementioned type within which the problem of maintaining a proper neutral setting of the distributor valve is solved. A further object in accordance with the foregoing object is to provide a valve mechanism integrated in a rack type servo-steering a unit that is readily adjusted without disassembly to a neutral position from a location externally of the cylindrical housing enclosing the rack and valve piston.